Capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (“DRAM”) devices. Capacitors include two conductors, such as parallel metal or polysilicon plates, which act as electrodes. The electrodes are insulated from each other by a dielectric material. With the continual shrinkage of microelectronic devices, such as capacitors, the materials traditionally used in integrated circuit technology are approaching their performance limits. Silicon dioxide (“SiO2”) has frequently been used as the dielectric material in capacitors. However, with smaller and smaller capacitor area, SiO2 cannot be thinned to provide sufficient capacitance while maintaining low leakage. This deficiency has lead to a search for improved dielectric materials. High quality, thin dielectric materials possessing higher dielectric constants (k) than SiO2 are of interest to the semiconductor industry. Examples of materials having dielectric constants (k) greater than SiO2 include hafnium oxide (“HfO2”), zirconium oxide (“ZrO2”), and strontium titanate (“SrTiO3”). In general, dielectric materials with a higher dielectric constant also exhibit higher leakage currents. Dielectric materials are typically formed by chemical vapor deposition (“CVD”) or atomic layer deposition (“ALD”). However, CVD is unable to provide good step coverage and film stoichiometry in high aspect ratio containers. Therefore, CVD is not useful to fill high aspect ratio containers. While ALD provides good step coverage, current CVD and ALD techniques each produce high-k dielectric materials that have high leakage.
To produce a capacitor, a bottom electrode is formed on a semiconductor substrate and a dielectric material is deposited over the bottom electrode. The bottom electrode and the dielectric material are annealed, and a top electrode is formed over the dielectric material. The dielectric material is typically annealed before the top electrode is formed.
U.S. Pat. No. 7,101,754 discloses forming mixed dielectric films, composed of a high-k dielectric to produce a certain level of capacitance and a relatively lower-k dielectric to control leakage current, on a conductor material. The dielectric film having a composition of SiO2 and TiO2 made by a sol-gel process is applied onto a substrate using a spin-on technique. The discontinuous layer is annealed in the presence of a reactive species so that exposed portions of the conductor material are converted to an insulating material. However, forming the mixed dielectric films is difficult due to the, oftentimes, conflicting deposition requirements of the high-k dielectric and the relatively lower-k dielectric.